In internal combustion gasoline engines, reflected pressure waves (“compression waves”) are generated in the exhaust system, which are caused by catalytic converters, resonators, mufflers or changes in cross-sectional area of exhaust piping. These reflected pressure waves in the exhaust system adversely impact torque output over a range of engine speeds or RPMs (revolutions per minute). The impact from these pressure waves is greater with modern engine technologies with variable valve timing and/or lift wherein valve lift and duration is increased at higher engine speeds. Pressure waves typically reflect off the exhaust system and back toward the engine, sometimes resonating, and often creating zones of alternating high and low pressure waves. These pressure waves vary according to engine RPM, tuning, and other factors, resulting in optimum torque at a given engine speed, but impaired torque at higher or lower than optimum engine speeds.
Much effort has been expended devising ways to improve engine performance. Patents have been granted for engine tuning devices and aftermarket modifications to stock exhaust systems. For example, U.S. Pat. No. 5,050,378 to Clemmons describes an expansion chamber (divergent/convergent cone) for four cycle internal combustion engines. However, the Clemmons apparatus is beneficial only for engines that employ some additional mechanism to briefly and partially reopen the engine's exhaust valve(s) after the intake valves have effectively closed. This reflected pressure wave increases cylinder pressure immediately before combustion. However, in the absence of an auxiliary reopening of the exhaust valves as taught by Clemmons, i.e., in conventional four cycle engines, there is no benefit from reflected compression waves within the exhaust system.
Another example of efforts to improve exhaust apparatus, U.S. Pat. No. 6,840,037 to Oberhardt, discloses an exhaust pulse control device with a simple expansion chamber, described as resulting in increased engine torque over a range of RPMs. Oberhardt does not address the impact and/or contribution of pressure wave management in the catalytic converter. Another potential problem not addressed by Oberhardt is its use of exceedingly steep transition angles. In addition, Oberhardt neglects the need to manage the reflected pressure waves created by the convergent end of the expansion chamber, and makes no mention of providing for sound attenuation.
Due to these and other problems and potential problems, there is a need for improved four cycle internal combustion engine exhaust apparatus designed and constructed to achieve pressure wave management that increases engine torque over a wide range of engine RPM levels, preferably also integrating with emissions control devices. Accordingly, the invented four cycle internal combustion engine exhaust embodiments described herein would be useful and advantageous contributions to the arts.